Exercise machines that utilize a selectorized weight stack to resist the movements of a user are commonplace in homes and commercial workout facilities. A generalized stacked weight exercise machine includes a support structure, a selectorized weight stack, and a user-manipulated element, such as a handle or bar (e.g., a pull-down bar). The support structure supports the user-manipulated element and a selectorized weight stack. A vertical rod extending through the selectorized weight stack is coupled to the user-manipulated element by way of cable, belt, or other flexible linkage. The rod includes a plurality of horizontal channels therethrough. The selectorized weight stack also includes a plurality of horizontal channels, which each extend through a different weight in the stack, and a vertical channel, which accommodates the rod in its normal (resting) position. When the rod resides in its resting position, the rod's channels align with those provided through the selectorized weight stack. A user selects a desired output resistance by inserting a selector pin into the channel of a selected weight thus fixing the selected weight to the vertical bar. To subsequently move the user-manipulated element during the performance of an exercise, the user must exert enough force on the user-manipulated element to lift the selected weight, and the weights residing above it, from their resting position.
Exercise machines including selectorized weight stacks of the type described above are limited in certain respects. For example, due to the presence of the weight stack, such machines tend to be relatively heavy and cumbersome and consequently less desirable for residential use and for other applications wherein weight capacity is limited. In addition, the stacked weights may crack and possibly break if returned to their resting position too quickly. Stacked weight exercise machines may produce excessive noise during use. As a further limitation, inertia of the weight stack may result in undesirable fluctuations in resistance during the performance of an exercise, especially if the user moves the user-manipulated element in an abrupt manner.
To overcome the above-noted disadvantages, exercise machines have been developed that utilize alternative resistance means to oppose the movements of the user. Of these alternative resistance exercise machines, those employing resilient resistance means (e.g., bendable rods or elastic bands) have achieved the greatest commercial success. However, such resilient resistance exercise machines are also associated with a number of disadvantages. Such resilient resistance exercise machines are often relatively bulky, complex, and expensive to produce. In contrast to stacked weight exercise machines, which permit the selection of a desired weight by a relatively simple process (i.e., the insertion of a selector pin), resilient resistance exercise machines may require that the user perform several steps to select a desired resistance. Finally, many resilient resistance exercise machines do not provide a substantially constant or linear resistance profile through the user's full range of motion.
Considering the above, it should be appreciated that it would be desirable to provide embodiments of a user-adjustable resistance mechanism suitable for employment within an exercise machine that overcomes the above-noted disadvantages. In particular, it would be desirable to provide a user-adjustable resistance mechanism that would enable a user to select amongst a plurality of output resistances derived from a single input resistance utilizing, for example, an intuitive selection interface similar to that employed by traditional stacked weight exercise machines. It would also be desirable if, in certain embodiments, the user-adjustable resistance mechanism provided a substantially constant or linear resistance profile throughout the user's range of motion. Other desirable features and characteristics of the present invention will become apparent from the subsequent Detailed Description and the appended claims, taken in conjunction with the accompanying drawings and the Background of the Invention.